The present invention relates to apparatuses for perforating wells, such as oil and gas wells, and in particular to firing heads of perforating guns.
Perforating guns have an array of explosive charges thereon. The explosive charges can fire projectiles or form a jet of liner material (such as copper). The guns are lowered inside of a cased well to a depth containing a pay zone of oil or gas. The explosive charges are detonated wherein the casing is perforated at the pay zone. Upon the completion of the well, oil and gas can then flow through the perforations into the casing and up to the surface.
Great care is taken with the explosive charges in the perforating guns in order to prevent their accidental detonation. An accidental detonation with the gun on the surface could result in the injury of a crew member. An accidental detonation in the well in an undesirable location could result in a loss of production of the well. Therefore, initiators are used to better control the detonation of the perforating guns. One type of initiator is known as a detonator, which is an electrical device.
Detonators are initiated by an electrical current. An electrical current heats a resistive element inside the detonator to a temperature that is sufficiently high to ignite a charge inside of the detonator. The detonator is located physically close to an end of a detonating cord so as to ignite the detonating cord. When ignited, the detonating cord propagates the detonation from the detonator to fire the explosive charges that are distributed along the length of the perforating gun.
One type of detonator has a spring loaded pin or button on one end and an explosive charge on the other end. For safety reasons, the detonator is internally grounded until the button is depressed. Thus, when internally grounded, the detonator is in a safe mode and is unable to detonate. This type of detonator is conventional and commercially available as part number DET-3050-008 from Owen Oil Tools of Fort Worth, Tex.
The detonator is located in a detonating block, which is located in a firing head at an end of the perforating gun. The detonator is contained within the detonating block and is adjacent to an end of the detonating cord in the perforating gun. A long rod, or arming and contact pin, is used to press the button on the detonator in order to arm it. Thus, the detonating block secures the detonator in place adjacent to the detonating cord and positions the detonator relative to the arming and contact rod.
Conventional detonating blocks function as collars to hold the detonator in place. Consequently, conventional detonating blocks have a passage extending from one end of the block to the other. Upon detonation, some of the hot gases from the detonator and the detonating cord blow back in the direction of the arming and contact pin, damaging the pin and its associated spring in the process.
When the perforating gun is brought back out of the hole to the surface after a detonation, such damage must be fixed before the gun can be reused. Often times, a well requires multiple perforations, requiring the perforating gun to make more than one trip downhole. Minimizing the damage to the detonating mechanism minimizes turnaround time for the perforating gun on the surface and equipment loss.
It is an object of the present invention to provide a firing head for a perforating gun that has minimum damage during a detonation.
It is another object of the present invention to provide a firing head for a perforating gun that can be reused with a minimum amount of turnaround time and equipment.
The present invention provides a firing head for a perforating gun for use in downhole applications. The firing head comprises a detonating block and a detonator. The detonating block has a first end and a second end, with the second end being structured and arranged so as to be located adjacent to a detonating material. A central passage extends through the detonating block from the first end to the second end. The central passage is structured and arranged to receive a detonator. At least one venting passage extends from the central passage through the detonating block to an exterior of the detonating block.
In accordance with one aspect of the present invention, the central passage further comprises a collar for receiving a detonator, the collar having an inside diameter that is smaller than an inside diameter of a portion of the central passage that is located between the collar and the second end.
In accordance with another aspect of the present invention, there is at least one venting passage between the collar and the first end of the detonating block and at least one venting passage between the collar and the second end of the detonating block.
In accordance with another aspect of the present invention, the venting passage between the collar and the second end of the detonating block is larger than the venting passage between the collar and the first end of the detonating block.
In accordance with still another aspect of the present invention, the firing head further comprises a detonator located and restrained in the central passage.
The present invention also provides a firing head for a perforating gun for use in downhole applications comprising a sub having a first end and a second end. A pin is located in the sub and is axially movable therein. The pin has a head located adjacent to the second end of the sub. A detonating block is removably coupled to the second end of the sub. The detonating block has a first chamber that receives the head of the pin and a detonating chamber that is structured and arranged to be adjacent to a detonating material in the perforating gun. The detonating block has a retainer located between the chamber and the detonating chamber. A detonator is located in the retainer and extends into the detonating chamber. The detonator has an arming mechanism that is located in the first chamber in selective contact with the head of the arming and contact pin. There is at least one venting passage in the detonating block extending from the detonating chamber to an exterior of the detonating block.
In accordance with another aspect of the present invention, the firing head further comprises at least one venting passage in the detonating block extending from the first chamber to the exterior of the detonating block.
The present invention also provides a method of detonating explosive charges in a downhole perforating gun. An arming mechanism for a detonator is provided. The detonator is provided in proximity to a detonating material. The arming mechanism, the detonator and the detonating material are all located along a longitudinal axis. The detonator is detonated. Gases from the detonator are vented laterally of the longitudinal axis so as to minimize damage to the arming mechanism.
In accordance with one aspect of the present invention, the step of providing the detonator in proximity to a detonating material further comprises the step of providing the detonator in a holder. The step of venting gases from the detonator laterally further comprises the step of venting the gases through the holder.